There has heretofore been known a biaxially stretched polyester bottle obtained by biaxially stretch-blow-molding a preform of a polyester resin such as polyethylene terephthalate. Owing to its excellent transparency, surface luster, impact resistance and gas-barrier property, the biaxially stretched polyester bottle has been widely used as a container for containing various kinds of beverages, foods, liquid detergents, etc.
The biaxially stretched polyester bottle used for containing beverages, usually, has an average thickness of about 0.25 to about 0.30 mm. From the standpoint of decreasing the cost and weight, however, it has been desired to further decrease the amount of the resin that is used.
From the above point of view, therefore, JP-A-7-257534 is proposing a bottle-like container obtained by blow-molding in a manner that the body portion has an average thickness of not larger than 0.25 mm and that the average stretching ratio is not smaller than 10 times.
The weight of the bottle-like container can be decreased when it has a capacity as large as, for example, 5000 mL. However, it becomes difficult to decrease the weight when the container has a capacity which is relatively as small as 2000 mL or less. In producing the bottle-like container, further, attempts have been made to increase the average stretching ratio to be not smaller than 10 times in the biaxial stretch-blow-molding while the longitudinal stretching ratio is in an ordinary range of 2 to 2.7 times. If it is attempted to further increase the longitudinal stretching ratio, problems arise such as whitening due to over-stretching, peeling of lamination (delamination) and burst, making the forming difficult.
There has further been proposed a thin bottle attempting to decrease the weight by decreasing the thickness of some portions of the container. For example, JP-A-2001-122237 is disclosing a technology dealing with a bottle of about 500 ml setting an average thickness of the shoulder portion to be 0.2 to 0.3 mm, an average thickness of the body portion to be 0.02 to 0.05 mm, and forming transverse ribs on the body portion to increase the strength against deformation. When the bottle having a thickness that so greatly varies as above is to be stretch-blow-molded, however, it becomes necessary to form a preform having a varying thickness by injection-molding accompanied by a problem in that it becomes difficult to set the conditions for stretch-blow-molding the preform.
The applicant has further proposed in JP-A-2003-191319 a biaxially stretch-blow-molded bottle of polyester having an average thickness that was decreased to 0.1 to 0.2 mm. This biaxially stretch-blow-molded bottle is free from whitening that stems from the over-stretching; i.e., a self-standing thin bottle-like container is formed making it possible to decrease the amount of the resin that is used and to decrease the weight.